The present invention generally relates to catheters. The present invention further relates to catheters having sheaths with variable stiffness. The present invention still further relates to intravascular imaging catheters.
Percutaneous coronary interventions in patients suffering from coronary artery disease often involve deployment of a stent in order to keep open a coronary artery that supplies oxygenated blood to a patient's heart. An intravascular ultrasound imaging catheter may be used to assess adequacy of stent deployment, including the extent of stent apposition and determination of the minimum luminal diameter within the stent.
Current intravascular ultrasound imaging catheters having a mechanically rotating imaging core include an imaging window having a single flexural modulus. An imaging window having a single flexural modulus avoids measurement inaccuracies due to image artifacts that may be introduced by use of an imaging window having a variable flexural modulus, such as braided sleeves or extrusions of varying wall thickness. The flexural modulus, or stiffness, of the imaging window affects catheter pushability and catheter trackability. Pushability describes how a force transmitted longitudinally at the catheter proximal end is transferred to longitudinal movement of the catheter distal end. Trackability describes how easily the catheter is able to reach its destination (e.g., a coronary artery segment). The use of an imaging window with a single flexural modulus presents a trade-off between catheter pushability and trackability. Current intravascular ultrasound imaging catheters exhibit limitations in navigating some coronary arteries.
Safe and effective delivery of an intravascular ultrasound imaging catheter to a coronary artery requires an imaging window having sufficient pushability to reach the coronary artery and adequate trackability to navigate the tortuous coronary arteries. It would be advantageous if the stiffness of the imaging window could be varied with length in order to optimize the balance between catheter pushability and trackability. It would be further advantageous if the imaging window provides uniform imaging performance along its entire length.